In‐Ky Cho

Kangwon National University

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Sung‐Ho Song

Korea Rural Economic Institute

Keunsoo Lee

Inje University Busan Paik Hospital

Hye‐Jin Kang

The Behaviouralist (United Kingdom)

Hwan‐Ho Yong

Korea Rural Economic Institute

Kiju Kim

Daegu University

Gyusang Lee

Korea Institute of Energy Research

Lee Heuisoon

DUKSAN Neolux (South Korea)

Byung‐Doo Kwon

University of Central Oklahoma

Kwang-Jun Choi

Korea Rural Economic Institute

Hong-Jun Shin

Cooperative Institutions

Kangwon National University

Korea Institute of Geoscience and Mineral Resources

Rural Development Institute

Samsung (South Korea)

University of Ulsan

Korea Rural Economic Institute

Korea Institute of Civil Engineering and Building Technology

Seoul National University

Korea University

Korea Fisheries Resources Agency

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Inversion of Small Loop EM Data by Main-Target Emphasizing Approach

Geophysics and Geophysical Exploration (2006)

In‐Ky Cho Mikyung Kang Kiju Kim

Geologic noise, especially located at shallow depth, can be a great obstacle in the interpretation of geophysical data. Thus, it is important to suppress geologic noise in order to accurately detect major anomalous bodies in the survey area. In the inversion of geophysical data, model parameters at shallow depth, which have small size and low contrast of physical property, can be regarded as one of geologic noise. The least-squares method with smoothness constraint has been widely used in the inversion of geophysical data. The method imposes a big penalty on the large model parameter, while a small penalty on the small model parameter. Therefore, it is not easy to suppress small anomalous boies. In this study, we developed a new inversion scheme which can effectively suppress geologic noise by imposing a big penalty on the slowly varying model parameter and a small penalty on the largely varying model parameter. We call the method MTE (main-target emphasizing) inversion. Applying the method to the inversion of 2.5D small loop EM data, we can ensure that it is effective in suppressing small anomalous boies and emphasizing major anomalous bodies in the survey area.

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Frequency Sounding in Small-Loop EM Surveys

Geophysics and Geophysical Exploration (2003)

In‐Ky Cho Lim Jin-Taik

The small-loop electromagnetic (EM) technique has been used successfully for many geophysical investigations, particularly for shallow engineering and environmental surveys. In conventional small loop EM operating at small induction numbers, geometric sounding has been widely used because the depth of penetration of EM energy depends only on the source-receiver separation. Recently developed small loop EM system, however, measures the secondary magnetic field, , at multiple frequencies with a fixed source-receiver separation and frequency sounding is tried actively. In this study, we analyzed the behavior of in-phase and quadrature components of , for horizonal coplanar (HCP) configuration over two-layer models. Through this theoretical analysis, it was found that the in-phase component of is more suitable for frequency sounding than the quadrature component. But, the in-phase component of is too small to measure, especially in resistive and noisy environment like Korea. Using the fact that the quadrature component is much greater than the in-phase component and the difference of quadrature component of measured at two frequencies shows the same behavoir as the in-phase component, we suggested an alternative frequency sounding technique. Also, we defined an apparent conductivity, which reflects well the conductivity of subsurface layers.

Resistive touchscreen

Component (thermodynamics)

Quadrature (astronomy)

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3D Modeling and Inversion of Magnetic Anomalies

Geophysics and Geophysical Exploration (2013)

In‐Ky Cho Hye‐Jin Kang Keunsoo Lee Kwang-Beom Ko Jong‐Nam Kim

자력탐사자료의 3차원 역산법을 개발하였다. 자력탐사자료의 역산에서 가장 문제가 되는 점은 비유일해 문제와 방대한 계산시간이다. 일반적으로 자력탐사자료의 역산은 모델변수의 수가 자료의 수보다 훨씬 많아 비유일해 문제를 더욱 심화시키게 된다. 또한 자력탐사자료는 심도 분해능이 매우 낮다. 비유일해 문제를 극복하기 위하여 분해능이 높은 모델변수에는 큰 제한을 가하고, 작은 모델변수에는 약한 제한을 가하는 분해능 모델제한자를 제안하고, 이를 적용하여 분해능이 낮은 모델변수도 효과적으로 추정할 수 있었다. 또한 대형 행렬식을 웨이블릿 변환을 통하여 희소행렬로 변환하고, 역행렬의 계산에 병렬계산 방식을 적용하여 계산시간을 획기적으로 절감하였다. 수치실험을 통하여 개발된 3차원 역산알고리듬의 타당성을 검토하였다. 또한 금산 지역에서 얻어진 항공자력탐사자료의 역산에 적용하였다. We developed a method for inverting magnetic data to recover the 3D susceptibility models. The major difficulty in the inversion of the potential data is the non-uniqueness and the vast computing time. The insufficient number of data compared with that of inversion blocks intensifies the non-uniqueness problem. Furthermore, there is poor depth resolution inherent in magnetic data. To overcome this non-uniqueness problem, we propose a resolution model constraint that imposes large penalty on the model parameter with good resolution; on the other hand, small penalty on the model parameter with poor resolution. Using this model constraint, the model parameter with a poor resolution can be effectively resolved. Moreover, the wavelet transform and parallel solving were introduced to save the computing time. Through the wavelet transform, a large system matrix was transformed to a sparse matrix and solved by a parallel linear equation solver. This procedure is able to enormously save the computing time for the 3D inversion of magnetic data. The developed inversion algorithm is applied to the inversion of the synthetic data for typical models of magnetic anomalies and real airborne data obtained at the Geumsan area of Korea.

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Synthetic data

10.7582/gge.2013.16.3.119

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Delineation of leachate pathways using electrical methods: case history on a waste plaster landfill in South Korea

Exploration Geophysics (2019)

Sung‐Ho Song In‐Ky Cho Gyusang Lee Hwan‐Ho Yong Jae-Yeon Um

A waste plaster landfill site, established as a high-density polyethylene (HDPE) sheet pile surrounded by a slurry wall to isolate possible contaminants within the landfill, was investigated using electric survey techniques. A sheet pile is an effective barrier wall for contaminated leachate containment, unless there are damaged zones within the pile. However, the perfect insulating properties of the pile make it difficult to apply the electrical resistivity method to measure the containment ability of the pile. To locate damaged zones in the sheet pile, which can act as pathways for the contaminated leachate, a potential difference (PD) profiling technique was applied. Through three-dimensional (3D) modelling, PD profiling demonstrated efficacy in locating damaged zones in the sheet pile. Moreover, a 3D survey was conducted to delineate the leakage pathways through the sheet pile, as well as the leachate distribution throughout the landfill. Before the 3D inversion of measured resistivity data, erroneous data caused by the sheet pile were rejected to minimise distortion of the inversion results. 3D inversion showed the sheet pile to be highly resistive overall, especially at shallow depths; however, further inspection via PD profiling identified several areas of damage in the pile. These damaged zones from PD profiling coincided well with the low resistivity zones present near the surface in the 3D inverted image. Furthermore, major leaks were found below the burial depth of the sheet pile. Thus, it was demonstrated the PD profiling and 3D resistivity survey can locate damaged zones in the sheet pile and delineate leakage pathways over the landfill site.

Sheet pile

Electrical Resistivity Tomography

10.1080/08123985.2019.1700109

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The Crosshole Resistivity Method Using the Mixed Array

Geophysics and Geophysical Exploration (2002)

In‐Ky Cho Han Sung-Hoon Kiju Kim

Resistivity tomography has become an important tool to image underground resistivity distribution. This method has been widely applied to site investigation for engineering and environmental purpose. In resistivity tomography, various electrode arrays can be used and each array has both merits and demerits. For example, the pole-pole array has high signal to noise ratio (S/N ratio), but its resolution is too low. The dipole-dipole array has low S/N ratio, but its resolution is very high. The Pole-dipole may has intermediate Snf ratio and resolution. The modified Pole-dipole array, recently proposed, shows reasonable S/N ratio and resolution, which are comparable to the pole-dipole array. These electrode arrays except the pole-pole array, however, have the problem that the apparent resistivity can diverge at some special electrode Positions. Also, the Pole-Pole array may not reflect the doe resistivity of an anomalous body. In this study, we propose a new electrode array, mixed array, where pole-dipole and modified pole-dipole ways are selectively used with the relative positions of current and potential electrodes. The mixed array has the same level of S/N ratio and resolution as the pole-dipole array and the apparent resistivity does not diverge in the receiver hole. Furthermore, the apparent resistivity using the array can reflect the true resistivity of the anomalous body.

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Time-lapse inversion of 2D resistivity monitoring data with a spatially varying cross-model constraint

Journal of Applied Geophysics (2011)

Kiju Kim In‐Ky Cho

Inverse transform sampling

10.1016/j.jappgeo.2011.04.010

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Citations (26)

Resistivity Survey Using Long Electrodes

Geophysics and Geophysical Exploration (2016)

In‐Ky Cho Keunsoo Lee Yeon-Jung Kim Rae-Young Kim

일반적으로 전기비저항 탐사에서는 편의상 점 전원을 사용한다. 만약 철제 케이싱과 같이 긴 전극을 사용한다면 전기비저항 탐사의 탐사 깊이가 증가할 것으로 기대된다. 그러나 긴 전극을 사용하여 회득된 전기비저항 탐사 자료는 통상적인 자료 해석 프로그램으로 처리할 수 없다. 이는 긴 전극에 의해 생성된 1차 전위가 점 전원에 의한 1차 전위와는 서로 다르기 때문이다. 이 연구에서는 긴 전극을 여러 개의 연속된 점 전원으로 대치하는 새로운 전기비저항 탐사 자료 처리 방법을 제안하였다. 이 방법에 의한 전위 분포를 해석적/수치적 해와 비교한 결과, 유한 차분법이나 유한 요소법에 의한 긴 전극을 사용하는 전기비저항 탐사 모델링이 가능함을 확인하였다. Generally, a point source has been routinely used in the electrical resistivity measurements because of easy installation. If steel-cased wells are used as long electrodes, we can expect the better depth of investigation. However, the resistivity data with long electrodes can not be processed with a conventional inversion algorithm because a long electrode produces the different primary potential distribution compared with the point source. In this study, we proposed a new technique to process the electrical resistivity data with long electrodes by replacing the long electrode with a sequence of point electrodes. Comparing the potentials obtained from the technique with the analytic/numerical solution, we ensure that the proposed technique can be used for the numerical resistivity modeling based on the finite difference or finite element method.

10.7582/gge.2016.19.1.045

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Identification of leachate from livestock mortality burial using electrical resistivity and small-loop EM survey: case history

Exploration Geophysics (2015)

Sung‐Ho Song In‐Ky Cho Kwang-Jun Choi

Leachate from livestock mortality burial is harmful to the soil and groundwater environment and adequate assessment approaches are necessary to manage burial sites. Among the methods used to detect leachate, geophysical surveys, including electrical resistivity and electromagnetic (EM) techniques, are used in many engineering approaches to environmental problems, such as identifying contaminant plumes and evaluating hydrogeological conditions. Electrical resistivity, with a small-loop EM survey, was used in this study as a reconnaissance technique to identify the burial shape and distribution of leachate from livestock mortality burial in five small separate zones. We conducted a multi-frequency small-loop EM survey using lattice nets and acquired apparent conductivity values along several parallel and perpendicular lines over a burial site. We also compared geophysical results to the geochemical analysis of samples from both a leachate collection well and a downstream observation well within the study area. Depth slices of apparent conductivities at each frequency (obtained from the small-loop EM survey data) clearly identified the subsurface structure of the burial shape and the extent of leachate transport. Low-resistivity zones, identified from two-dimensional (2D) electrical resistivity imaging results, were matched to the five burial zones (within a depth of 5 m), as well as high electrical conductivity of the leachate obtained from leachate collection wells, and depth slices of the apparent conductivity distribution obtained from the small-loop EM survey. A three-dimensional (3D) inversion of resistivity data provided a detailed 3D structure of the overall burial site and leachate pathways. Moreover, these zones were widely spread over the burial site, indicating that leachate potentially extended through damaged regions of the composite liner to a depth of 10 m along the downstream groundwater flow. Both the small-loop EM method and the electrical resistivity method were considered suitable for identifying the shape of the livestock mortality burial and the extent of leachate.

Electrical Resistivity Tomography

10.1071/eg14111

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Discussion: On ‘Negative apparent resistivity in dipole–dipole electrical surveys’ (Jung, H.K., Min, D.J., Lee, H.S., Oh, S.H., and Chung, H., Exploration Geophysics, 40, 33–40)

Exploration Geophysics (2010)

In‐Ky Cho Jungho Kim

Corresponding author. Email: choik@kangwon.ac.krThe DC resistivity method is a well known geophysicalexploration technique and is widely applied in miningexploration, groundwater surveys, and engineering andenvironmental investigations. Negative apparent resistivities,especially in 2D surface dipole–dipole surveys, are oftenobserved and generally have been regarded as measurementerrors or the effect of noise. Cho et al. (2002) insisted that ifthe earth is isotropic and ﬂat, and the survey line is straight,apparent resistivity is always positive regardless of subsurfacestructures. On the contrary, Jung et al. (2009) insisted thatnegative apparent resistivity could be caused by a geologicalstructure. In this discussion, we re-examine the possibility ofnegative apparent resistivity since the conclusions of these twopapers are entirely contrary. We assume that a 2D resistivitysurvey is performed alongastraight lineonthe ﬂat surface of anisotropicearth,asJungetal.similarlyadopted.Weﬁrstdescribethe behaviour of surface charge, electric ﬁeld, potential, andcurrent inside and outside an inhomogeneity. We carry out 3Dﬁnite-elementmodellingforthesameU-shapedmodelpresentedby Jung et al. as a typical model that yields negative apparentresistivity.Then,wecompareourresultwiththatofJungetal.anddiscuss whether negative apparent resistivity is really possibleunder the stated conditions.First,letusexplainthebehaviourofelectricﬁeldandpotentialdifference. Suppose that an inhomogeneity with resistivity ris surrounded by a uniform medium having resistivity r

10.1071/eg10005

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SP Monitoring at a Sea Dike

Near Surface Geophysics (2013)

Hye‐Jin Kang In‐Ky Cho Jungho Kim Hwan‐Ho Yong Sung‐Ho Song

ABSTRACT The self‐potential (SP) method is widely used in seepage evaluation hydrological studies to monitor the integrity of infrastructure such as dams, sea dikes, and other types of flood control devices because the electric signals that are measured are directly related to seepage rate. At leaking areas along sea dikes, large SP anomalies can be generated by the rising and falling of tides. Unfortunately, SP data are often contaminated with several types of noise, such as that from drifting electrodes, telluric disturbances, and external electrical noise. Furthermore, SP signals can have high levels of spatial variability due to heterogeneity in lateral resistivity at the locations where the electrodes are installed. Because of these issues, it is very difficult to correlate the measured SP voltages with the streaming potentials associated with groundwater flows at particular points in time. To alleviate these problems, we developed a simple but effective interpretation method for SP monitoring data that involves subtracting consecutive SP voltages collected at different time points from a particular monitoring station. This subtracting procedure is able to effectively reduce spurious SP anomalies caused by electrode drift, change in resistivity, and other types of interference. Therefore, any changes observed in SP measurements over certain time frames were interpreted as resulting primarily from temporal changes in seepage flow. To demonstrate the performance of this method, we analysed SP monitoring data measured at a sea dike located on the southern coast of Korea. Our results confirmed that the SP interpretation method is able to explain changes in streaming potentials depending on the tide change over time and to detect the horizontal location of anomalous seepage zones along the sea dike.

Dike

Economic geology

Spurious relationship

Classification of discontinuities

Gemology

10.3997/1873-0604.2013063

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Citations (6)